Implantation signals a massive cellular response in the uterus. Among the major cell types that expand in response to pregnancy are macrophages, cells with both primitive and highly sophisticated functions. Macrophages that arrive via the blood or replicate in situ distribute themselves into specific anatomic compartments of pregnancy tissues, where they display distinct sets of phenotypic markers. The function(s) of uterine macrophages are unknown although their counterparts in other tissues protect against infection, a primitive function, and display or secrete molecules with powerful regulatory effects on other cells, a highly sophisticated function. This study is based on the postulate that uterine macrophages and invading trophoblast cells exert reciprocal influences over one another as the placental bed is established, maintained, and at term, dissolved. Preliminary data have been acquired which suggest that trophoblast cells are targets for some macrophage-derived molecules, and that trophoblast cells may influence some major macrophage activities. Preliminary data were generated in a rat model in which macrophages and their soluble products were cocultured with trophoblast cells in vitro. The proposed studies use the same general approach: uterine cells are harvested from pregnancy tissues (decidua, metrial gland, uterus) at mid to late gestation as well as from deciduoma and are fractionated into macrophage-enriched and macrophage-depleted populations; placental cells are represented by trophoblast cell lines derived from midgestation placentas of outbred and inbred rats and freshly harvested cells from mid to late gestation placentas. Both direct cellular effects and the effects of soluble molecules are tested using in vitro assays that focus on specific cellular activities, primarily proliferation and migration. Testing includes determining which molecules are normally synthesized by uterine macrophages (products of arachadonate metabolism, interleukin-1, tumor necrosis factor-alpha, colony stimulating factors). Identification of specific regulatory molecules is made by using highly purified and recombinant macrophage-derived molecules and monoclonal antibodies to those molecules. The mechanisms by which regulation is accomplished will be explored using cytotoxicity assays, determination of changes in ploidy and expression of specific markers, cAMP assays, and evaluation of proto-oncogene expression. Do negative macrophage-derived regulatory molecules prevent a dangerous influx of trophoblast cells into maternal tissues? Do positive regulatory molecules enhance successful pregnancy stimulating trophoblast cells? Future therapeutic interventions in cases of excessive trophoblast invasion (hydatidiform mole, choriocarcinoma) and in cases of chronic pregnancy failure may rely on the findings made in this study of uterine macrophages and similar studies addressing the roles of other types of uterine cells.